The cataphractarii, a particular type of cavaliers

The cataphractarii were soldiers of the cavalry protected by a metal or reinforced leather armour. Ancient romans discovered this kind of soldiers around the first century a.D., when they kept in contact with Sarmati Rossolani people, at the Danubian border.
This type of soldiers, in addition to the armor, were equipped with a very heavy spear, 3 meters and half long and handled with both hands. They did not use any shield, and their charges were quite slow, but unstoppable. The effect on the enemy was more psychological than physical.
It was Emperor Adrian who formed the first official unity of cataphractarii in the Roman army.

Bibliography: The Roman army by Chris McNab